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What is a Forced Draft?

C.L. Rease
C.L. Rease

A forced draft uses fans to increase air flow and pressure in cooling towers, boilers and other types of heating equipment by increasing air movement. Increased air flow allows combustion-style heating equipment to burn fuel more effectively and removes heat build up from around water sitting in a cooling tower. Force draft fans are designed for specific types of equipment and are housed in a metal sleeve that eliminates leaks from forming around the fan as pressure builds inside the piece of equipment. Installing the correct forced draft fan for a specific piece of equipment is vital to the success of the fan in increasing draft.

Draft inducers are a type of forced draft fan that mounts inside the boiler breaching carrying fumes and exhaust from a burning boiler. A natural draft exists inside of the boiler breaching, but natural draft has a variety of factors the limit the amount of exhaust pulled from the combustion chamber of a boiler. An installed draft inducer creates a forced draft away from a boiler's combustion chamber. As the exhaust gases are pushed through the breaching, more air enters the combustion chamber through the air intake vents. Another type of forced fan works with a draft inducer to further increase the efficiency of a boiler.


Intake fans are forced draft fans that increase the pressure inside a boiler's combustion chamber. Increased combustion chamber pressure allows the fuel inside the boiler to burn more efficiently and reduces the waste associated with incomplete combustion. This type of fan either mounts to the outside of the boiler body or sits inside the intake duct on larger commercial-style boilers. Sitting in front of the intake is a filter designed to reduce the amount of pollutants entering the boiler through the intake fan and keep the intake fan clean. Dirt collecting on the blades of an intake fan reduces the amount of air the fan can feed into the boiler combustion chamber.

Cooling towers of coal-fired power plants use heat to convert water to steam and create energy. The water used in the power plant comes from a local body of water, cycles through the plants combustion chamber and then returns to the body of water. Forced draft fans move large quantities of air through the plant's cooling towers to cool the heated water to a temperature close to the water's natural temperature. These fans are large and mount in series on the top section of the cooling tower. All types of forced draft fans require maintenance to ensure proper operation.

Discussion Comments


A forced draft fan is industrial equipment.

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